i would move the #6 coil pack around to see if it follows it, that would tell you if its that. if you have the tools i would check what each cylinders fuel pressure is, if you wanted to take more of a shot in the dark you could just run sea foam through your engine to clean the fuel system.

also im assuming that your maintenance is all up to date, that means new:
plugs
wires
fuel filter
clean maf

if you havent done those things do them first